Confirmed: Windows Vista throttles back network when playing video

A Microsoft employee has confirmed that Windows Vista will scale back network …

Mark Russinovich, the man who first identified the Sony rootkit and more recently was hired by Microsoft to work on their operating system team, has a new post in his blog that explains the drop in network performance that some Windows Vista users have been experiencing when playing back multimedia files.

According to Russinovich, this is by design. Vista contains a new service called "Multimedia Class Scheduler" that detects when music or video files are being played back and throttles back network performance to avoid any hiccups in playback. It only kicks in on gigabit Ethernet connections, so those still on 10/100Mbps networks shouldn't ever notice it happening. Also, it only affects file transfers over LAN—Internet surfing and downloads are unaffected. Russinovich states that if both the receiving and sending computers have gigabit adapters, network throughput will drop to about 15 percent.

The new limit was put in after "experiments that reliably achieved glitch-resistant playback on systems with one CPU on 100Mb networks with high packet receive rates." Russinovich states that the new hard-coded limit may be "short-sighted with respect to today’s systems that have faster CPUs, multiple cores and Gigabit networks" and that Microsoft will continue to tweak it in the future.